1. Field of the Invention
The present invention relates to a broadcasting/telecommunication convergence system, and more particularly to an optical network unit for an access network.
2. Description of the Related Art
Currently, telecommunication and broadcast subscribers use data services, such as ultra-high speed Internet services, through an asymmetric digital subscriber line (ADSL), a very high bit-rate digital subscriber line (VDSL), an Ethernet local area network (Ethernet LAN), or a cable modem. Such subscribers can access broadcast services through cable broadcasts and satellite broadcasts based on a hybrid fiber coaxial (HFC). This, however, means that the subscribers employ mutually different media in order to use telecommunication and broadcast services. It is noted that the data rates of the telecommunication services are several Mb/s.
Accordingly, it is necessary to employ an FTTH system connected to a home through optical fiber in order to provide subscribers with both high speed and large capacity communication and broadcast services by overcoming limits of a conventional technique. Such FTTH systems for providing such high speed and large capacity communication and broadcast services are classified into passive optical networks (PONs) and active optical networks (AONs).
The above-mentioned conventional technique for an access network is mainly achieved through being based on either an ATM network or an Ethernet network. In particular, the ATM network has a transmission advantage suitable for broadcast. Recently, a transmission method such as an ATM passive optical network (APON), which merges an ATM technique with an access network, has been developed. However, the ATM technique indispensably employs a high-priced ATM switch. For this reason, it is difficult to construct a low-priced access network. Also, although an Ethernet technique may ensure relatively low-priced access networks, it may lower quality of service (QoS) for broadcast data.
A conventional broadcast/telecommunication convergence fiber to the home (FTTH) system using time divisional multiplexing (TDM) as shown in FIG. 1 has been proposed to converge broadcast and telecommunication. The broadcast/telecommunication convergence FTTH system shown in FIG. 1 includes an optical line terminal (OLT) 300, an optical network unit (ONU) 400, and a gateway 500.
Components for converging broadcast and telecommunication perform the following operations.
The OLT 300 receives information of a digital broadcast 100 through an external broadcast network and information of external data communication (VOD, Internet, etc.) 200. The received signals are electro-optically converted into optical signals and are transferred through optical wavelength division multiplexing (optical WDM).
The ONU 400 receives the WDM optical signals from the OLT 300. The WDM signals are opto-electrically converted after WDM demultiplexing the WDM optical signals into broadcast signals and communication signals. The ONU 400 processes upstream information delivered from users to transfer the broadcast signals and communication signals selected by each user by performing time division multiplexing with respect to the broadcast signals and communication signals.
The gateway 500 performs time division demultiplexing (TDDM) with respect to the time division multiplexed signals delivered from the ONU 400 to divide the time division multiplexed signals into signals of each service. In addition, the gateway optically transfers upstream information from a user to the ONU 400.
In more detail, the OLT 300 includes a broadcast multiplexer (Mux) 101 for receiving and multiplexing digital broadcasts, an optical transmitting unit 102 for converting the multiplexed digital broadcast into optical signals, and a communication switch 103, which receives signals from an Internet/VOD (video on demand) 200 to perform switching downwardly and switches upward communication signals from each subscriber to the Internet/VOD 200 network. The OLT 300 also includes an optical receiving unit 105 for receiving upward optical signals to convert the received upward optical signals into electrical signals, and a wavelength divisional multiplex (WDM) 106 for wavelength divisional multiplexing with respect to signals so as to transfer the signals.
The ONU 400 includes a wavelength divisional demultiplexer 107 for dividing optical signals delivered from the OLT 300 into broadcast signals and communication signals, a broadcast demultiplexer (demux) 108 for dividing the broadcast signals divided by means of the wavelength divisional demultiplexer 107 into signals of each broadcast channel, and a broadcast switch 109 for switching the divided signals input into each broadcast channel according to selection of subscribers. The ONU 400 also includes a communication switch 112 for switching downstream communication signals divided by means of the wavelength divisional demultiplexer 107 according to the subscribers and for delivering upstream communication signals received from subscribers to the OLT 300, time divisional multiplexers (TDMs) 110-1 to 110-n for performing time divisional multiplex with respect to the broadcast signals and the communication signals switched according to the subscribers, and optical transmitting/receiving units 111-1 to 111-n for delivering the broadcast signals and communication signals multiplexed by means of the TDMs 110-1 to 110-n to the subscribers (gateways) and for delivering upstream signals from subscribers to the communication switch 112 through the TDMs 110-1 to 110-n. 
In addition, each gateway 500 includes a transmitting/receiving unit 113 for receiving downstream signals from the ONU 400 and for transmitting upstream signals to the ONU 400, and a time divisional demultiplexer (TDDM) 114 for dividing the time divisional multiplexed broadcast signals and communication signals into communication signals and broadcast signals. The gateway 500 also includes a communication switch 115 for receiving the communication signals from the TDDM 114 to deliver the communication signals to communication units, such as an Internet/PC 118 of a subscriber, and for delivering upstream signals from the communication units such as an Internet/PC 118 of the subscriber, etc., to the ONU 400.
In this regard, each subscriber watches a digital TV 117 by decoding the broadcast signals delivered from the TDDM 114 through a set top box (STB) 116 and can access to a network by transmitting/receiving communication signals by means of the Internet/PC 118 of a subscriber.
However, according to the conventional broadcast/telecommunication convergence FTTH system, the broadcast signals and the communication signals, which are time division multiplexed, are delivered for a connection between the ONU 400 and the gateway 500. The time division multiplexed broadcast signals and communication signals are then demultiplexed. The conventional broadcast/telecommunication convergence FTTH system causes fault to parts having multi-channels of the broadcast signals and parts receiving broadband communication signals.
In more detail, the conventional broadcast/telecommunication convergence FTTH system employs a TDM method, which transmits signals from the ONU 400 to the gateway 500 of a subscriber side by combining communication signals (e.g., Ethernet data) with broadcast signal selected by a subscriber in one time frame. The time frame is created through a field programmable gate array (FPGA). The FPGA only receives Ethernet signals having a data rate of about 100 Mbps and two-channel high definition (HD) broadcast signals in maximum because the FPGA has a limitation for processing data. In particular, the FPGA is designed to receive broadcast signals having a fixed length.
It cannot, however, provide broadcast signals in accordance with various standards (e.g., broadcast signals having different wavelengths) or broadcast signals having more than three channels even if a subscriber requests the broadcast signals.
In addition, the broadcast switch 109 provided in the broadcast/telecommunication convergence FTTH system shown in FIG. 1 includes two cross point switches coupled with each other.
The broadcast/telecommunication convergence FTTH system branches serialized MPEG2 transport streams (TSs) into two MPEG2 TSs, selects a TS having a program required by a subscriber by using the two cross point switches, and combines the two MPEG2 TSs into one stream in a TDM module. As a result, two programs required by a subscriber can be transferred through the above-described procedure.
However, such a method for transferring two MPEG TSs required by a subscriber through a TDM mode is problematic because the number of video screen images for one subscriber is fixed according to the number of ports of the broadcast switch 109 assigned to the subscriber and the number of input streams specified through FPGA for the TDM. Accordingly, it is not possible for a network administrator to flexibly manage a system according to various requirements of subscribers.
In addition, in order to improve transmission efficiency when transferring broadcast data, an upper-class network must transfer the broadcast data by combining each MPEG2 TS including a plurality of programs into one multi-program transport stream (MPTS). The MPTS created as described above has a bit rate varied depending on service media, such as a digital media center (DMC), a satellite, a terrestrial broadcasting, etc., and service methods thereof. Thus, it is not possible to apply the MPTS to a TDM method, which outputs data with a constant bit rate by requesting a fixed input data bit rate. To solve the above-mentioned problem, it is necessary to install a plurality of expensive MPEG REMUX apparatuses.